Page:Popular Science Monthly Volume 50.djvu/516

498 seeds being ripened and the bud scales formed over the tender tips of the branches long before the first severe frost appears.

Let us now glance at those higher forms of life called animals—"higher," because they are absolutely dependent upon plants for their food—and see how they pass away their time while their food-producers, the plants, are resting.

Beginning with the earthworms and their kindred, we find that at the approach of winter they burrow deep down where the icy breath of the frost never reaches, and there they live during the cold season a life of comparative quiet. That they are exceedingly sensitive to warmth, however, may be proved by the fact that when a warm rain comes some night in February or March, thawing out the crust of the earth, the next morning reveals the mouths of hundreds of the pits or burrows of these primitive tillers of the soil in our dooryard, each surrounded by a little pile of pellets, the castings of the active artisans of the pit during the night before.

If we will get up before dawn on such a morning we can find the worms crawling actively about over the surface of the ground, but when the first signs of day appear they seek once more their protective burrows, and only an occasional belated individual serves as a breakfast for the early birds.

The eyes of these lowly creatures are not visible, and consist of single special cells scattered among the epidermal cells of the skin, and connected by means of a sensory nerve fiber with a little bunch of nervous matter in the body. Such a simple visual apparatus serves them only in distinguishing light from darkness, but this to them is most important knowledge, as it enables them to avoid the surface of the earth by day, when their worst enemies, the birds, are in active search for them.

The fresh-water mussels and snails and the crayfish burrow deep into the mud and silt at the bottom of ponds and streams where they lie motionless during the winter. The land snails, in late autumn, crawl beneath logs, and, burrowing deep into the soft mold, they withdraw far into their shells. Then each one forms with a mucous secretion two thin, transparent membranes, one across the opening of the shell and one a little farther within, thus making the interior of the shell perfectly air-tight. There for five or six months he sleeps free from the pangs of hunger and the blasts of winter, and when the balmy breezes of spring blow up from the south he breaks down and devours the protecting membranes and goes forth with his home on his back to seek fresh leaves for food and to find for himself a mate.

Next in the scale come the insects, which comprise four fifths of all existing animals, and each one of the mighty horde seen in summer has passed the winter in some form. One must look for